750's are long dead...
Just don't tell Suzuki. Seriously, 750's appear to get relatively small amounts of factory support, but can you blame them? Not only are they not as fast on the track, they're not as fast on the sales floor. Kids buy 750's if the dealership can't get them the lastest GRPDQ-1000 or if they can't afford it. Period. Yes, more mature riders sometimes buy 750's if it fits their needs better than 600's or 1000's, but most sport bike riders are anything but mature. (And thank god for them and all the spare parts they generate with frequent wrecks.)
I agree that if the AMA wants inline 4's to be competetive again they'll need to change the rules, I just hope they'll do it in a manor that doesn't kill the twins.